Neer coined the term cuff tear arthropathy in 1972 to describe the arthritic, eroded/collapsed condition of the glenohumeral joint following prolonged/progressive subacromial impingement resulting from massive, full thickness rotator cuff tears. This pathology is associated with extreme pain and near complete loss of function. (see Neer, C. S. et al. Cuff Tear Arthropathy. JBJS. #65: 1232-1244. 1983).
Cuff tear arthropathy has been historically treated with acromioplasty, arthroscopic debridement, tendon transfers, humeral tuberoplasty, arthrodesis, total shoulder arthroplasty (constrained, semi-constrained, or unconstrained), bipolar shoulder arthroplasty, hemiarthroplasty (with and without acromial spacers), and most recently (and successfully) reverse shoulder arthroplasty.
The Reverse/Inverse shoulder was first conceived by Neer in the early 1970's to treat patients suffering from CTA; specifically, this device was intended to provide pain relief and prevent progressive acromial, coracoid, and glenoid erosion by resisting humeral head superior migration. This was theoretically accomplished by inverting the male and female ball and socket so that the glenoid component was now convex and the humerus now concave; doing so created a physical stop that prevents the humerus from migrating superiorly. Several reverse shoulder designs have since been conceived and developed: the Fenlin, Reeves, Gerard, Kessel, Kolbel, and the Neer-Averill to name but a few; of these, only the Kessel design has reported long-term outcomes (it is believed that each of the aforementioned designs have since been abandoned). Similar to constrained total shoulder arthroplasty, the fixed center of rotation resulted in an excessive torque on the glenoid that compromised fixation, ultimately leading to loosening.
In 1987, Paul Grammont introduced a new reverse shoulder design. It consisted of 2 components: the glenoid was a metallic or ceramic 42 mm ball (˜⅔ of a sphere) and the humeral component was a polyethylene “trumpet-shaped” cup (whose concave surface was ˜⅓ of a sphere); the humeral component was fixed with PMMA. The preliminary results of this prosthesis were published in 1987 (see Grammont, P. M. et al. Etude et Realisation D'une Novelle Prosthese D'Paule. Rhumatologie. #39: 17-22. 1987); after a mean follow-up of six months, all six patients (8 shoulders) were pain-free; however, mobility was variable: 3 patients had active anterior elevation between 100-130°, 3 patients had active anterior elevation less than 60°. These inconsistent results necessitated a redesign.
In 1991, the Grammont reverse shoulder was redesigned and renamed as the Delta III reverse shoulder prosthesis. The cemented glenoid failed; therefore, the glenosphere was redesigned to have a fixed central peg and divergent screws. The ⅔ of a sphere in the glenoid was abandoned for ⅓ of sphere to place center of rotation directly in contact with glenoid fossa; thereby, reducing the torque on the bone surface. The humeral component was designed for either cemented or uncemented applications (see Boileau, P. et al. Grammont Reverse Prosthesis: Design, Rationale, and Biomechanics. JSES January/February: 147S-161S. 2005).
This prosthesis was called the “Delta” because of its functional dependence on the Deltoid. The design rationale for the Delta III is described as follows:                the center of rotation is shifted medially (to increase the effective lever arm of the deltoid by recruiting more of the deltoid fibers for elevation and abduction).        the center of rotation is shifted distally by lowering the humerus (to tension the deltoid).        the center of the glenosphere is placed directly on the glenoid fossa to limit the torque on the fixation devices and resist loosening.        the inverted concavities of the glenohumeral joint create a physical stop to prevent humeral head superior migration; the status of the CA arch is irrelevant with this design.        
Whether these theoretical biomechanical benefits of the Delta will actually become realized has yet to be determined as there has been limited long-term outcome studies (>5 yrs) which demonstrate its reliability; however, short-term and medium-term outcome studies suggest that the design provides pain relief and restores function (primarily in abduction/adduction and partially in flexion/extension; internal/external rotation is restored on a limited basis dependant upon the condition of the infraspinatus and the teres minor). In this regard, see the following: Boileau, P. et al. Grammont Reverse Prosthesis: Design, Rationale, and Biomechanics JSES January/February: 147S-161S. 2005; Rittmeister, M. et al. Grammont Reverse Total Shoulder Arthroplasty in Patients with Rheumatoid Arthritis and Nonreconstructable Rotator Cuff Lesions. JSES. January/February: 17-22. 2001; Vanhove, B. Grammont's Reverse Shoulder Prosthesis for Rotator Cuff Arthropathy. A Retrospective Study of 32 Cases. Acta Orthop Belg. #70 (3): 219-225. 2004; Sirveaux, F. et al. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. JBJS 86-B: 388-395. 2004; Katzer, A. Two-Year Results After Exchange Shoulder Arthroplasty Using Inverse Implants. Orthopedics. Vol. 27, #11: 1165-1167. 2004; Walch, G. The Reverse Ball and Socket: When is it Indicated? Orthopaedics Today. pp. 18-20.
Of note, the Delta reverse shoulder is associated with a number of different types of complications including glenoid loosening, scapular “notching” (more descriptively called inferior glenoid erosion), acromion fractures, dislocation (head from poly and poly insert from humeral stem), instability, humeral stem fracture, humeral stem loosening, and glenoid screw fracture. In this regard, see the immediately preceding cited references.
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof.